It is well known that hot-melt adhesives comprising a base of a polymer such as a polyolefin, a polyamide, a polyester, a vinyl acetate copolymer, a cellulose derivative, polymethyl methacrylate, a polyvinyl ether or a polyurethane and, added to the base, a tackifier, exhibit adhesive effect when applied to, for example, a label, a kraft tape or a cloth tape and heated.
In recent years, the fields of application of hot-melt adhesives are rapidly increasing because the hot-melt adhesives are superior to the conventional solvent containing adhesives in the coating speed, safety, working environment and energy saving. Commonly employed hot-melt adhesives comprise a base polymer of EVA or a styrene/conjugated diene block copolymer added to the base polymer, a tackifier and a low-molecular-weight polyolefin. Enhanced performance of adhesives is increasingly demanded in recent years and it is required that adhesives exhibit high adhesive strength to a variety of materials.
For example, specifically, the styrene content of the adhesive based on the styrene/conjugated diene block copolymer is increased for improving the heat resistance of the adhesive. However, the adhesive strength of the resultant adhesive is not satisfactory, and it has been difficult to realize a desirable balance of heat resistance and adhesive property for the adhesive.